Helium permeable containers

ABSTRACT

An alpha-emitting radioisotope source container which allows for the controlled release of helium gas without permitting any radioactive material to escape, the container being a metal-fiber composite of helium impermeable metallic wall means with helium permeable quartz fibers reinforcing the wall means and extending continuously through at least a portion of said wall means and providing a fibrous helim leak path.

ilite Frank et al.

[ 1 Feb.29,1972

HELHUM PERMEABLE CONTAINERS Louis Frank, Baltimore; Harry P. Kliug,Glenarm, both of Md.

Assignee: Hittinan Associates, Inc., Baltimore, Md.

Filed: July 28, 1966 Appl. No.: 568,597

lnventors:

Related US. Application Data Continuation-impart of Ser. No. 454,542,May 10, 1965, abandoned.

U.S.Cl ..29/l82.5,161/143,161/158, 250/845, 29/133 int. Cl ..G21c 13/00Field of Search ..176/79; 250/845; 29/1825, 29/183, 191.2; 75/200 F;313/180; 161/158, 143

References Cited UNITED STATES PATENTS Carroll ..,..,...,....,29/ 2.s-

3,019,103 l/l962 Alexander et al ..29/l82.5 3,047,383 7/1962 Slayter....29/l 82.5 3,246,191 4/1966 Frentop.... ....250/84.5 3,256,596 6/1966Fiedler ....75/200 F Primary Examiner-Carl D. Quarforth AssistantExaminerB. H. Hunt Attorney-Fleit, Gipple & Jacobson [5 7] ABSTRACT ofsaid wall means and providing a fibrous helim leak path.

7 1 6 Claims, 1 Drawing Figure HELIUM PERMEABLE CONTAINERS Thisinvention relates to a technique for allowing helium gas, the product ofalpha emitting radioisotopes used in nuclear power sources, to escapefrom its container without permitting the radioactive material to bereleased; and is a continuation-in-part of our application, Ser. No.454,542, filed May 10, l965, and now abandoned.

Radioactive isotopes whose decay heat is converted to electricity bythermoelectric or thermionic converters are used in compact, highoutput, energy devices. Alpha particle emitting isotopes are desirableheat sources because of their high thermal outputs, and ease of handlingfrom a safety viewpoint. Alpha sources do have serious limitations whenone considers the buildup of gas pressure within the source container asthe decaying isotope emits alpha particles which are helium nuclei. Thiscontinuous pressure buildup limits the life of the radioisotope devicesince the creep resistance of the container material operating atelevated temperatures, can be exceeded and the container can rupture.The use of a void volume within the container or venting of thecontainer have been suggested as methods for circumventing the heliumbuildup problems. Both of these methods compromise the objectives ofcompactness, simplicity, and safety is radioisotope devices.

The principal object of this invention is to be able to construct alphaemitting radioisotope source containers which allow for the controlledrelease of helium gas without permittin g any radioactive material toescape from the container. This controlled release of helium gas willpermit one to adjust the internal container pressure to any desiredlevel.

A further object and advantage of this invention is that the means ofproviding helium permeation through the container can also be used tostrengthen the container.

The FIGURE of drawing illustrates one shape of a container made in aform to carry out this invention.

The container can be in any form but is shown for purposes ofillustration, in the form of a tubular member 2, surrounding radioactivematerial space 1. Container 2 has an end wall 3 formed to be placedinside of tubular member 2 and secured in sealed relationship withmember 2 around the periphery thereof by welding or other forms ofcontinuous bond as shown at 4.

The objective can be achieved by incorporating in the container materiala substance through which heliummay permeate and said substance will bein such a form as to enhance the strength of the container. Fused quartzin the form of fibers distributed in the container material is the typeofsubstance which can provide the helium leak path and strengthimprovement to the container. The fibers should be continuous throughthe material of the wall from the inside to the outside thereof.

While most constructional materials have been known to be impermeable tohelium, the use of glasses in ultrahigh vacuum systems has indicatedhelium permeation through glasses. Helium diffusion through glasses hasbeen measured and the permeation velocity constant K has beenexperimentally determined. The following table presents the heliumpermeation constants at various temperatures of fused quartz (100percent SiO which has the highest measured permeation rate.

K, the unit of the permeation rate can be expressed as cc.(STP)/sec./cm. area/ mm. thickness/cm. Hg pressure difference.

It is seen from the above tabulation that it is possible to relieve thegas pressure in the interior of an alpha emitting container by providinghelium permeable members through which helium is free to permeate. For aplanar member, with pressure gradient p, cross-sectional area A, andthickness d, the quantity of gas q, per unit I, to pass through it isgiven by Knowing the permeation velocity constant K at a specifictemperature, and the quantity of gas 4 being generated per unit timewithin a radioisotope container, it is possible to construct a containersuch as shown in the drawing, with helium permeable members such asquartz fibers with controlled cross-sectional area and thickness andthereby maintain any desired pressure within said container.

This type of construction is based on the technology known as fibercomposites. Fiber composite structural components are prepared byincorporating high strength fibers into a ductile metal matrix andthereby reinforcing the strength of the matrix. This approach has beenvary successful in improving the high temperature strength of metals byincorporating ceramic fibers in the body. Aluminum oxide whiskers insilver exhibit a tensile strength of nearly 45,000 p.s.i. at 1,400 F.which is more than 20 times that of pure silver.

The container construction proposed in this invention can be ofpractically any shape but for the purpose of illustrating an embodimentof a container is shown cylindrical in shape and consisting of quartz orother helium permeable materials in fibrous form incorporated intometallic alloys such as molybdenum, tungsten, tantalum, columbium,titanium, nickel or cobalt metals or their alloys based upon them ornoble metals such as gold, silver or platinum or noble metal basedalloys such as platinum-rhodium or platinum-iridium or platinum-osmiumto form a composite. The cylindrical portions of the container can beprepared by aligning the fibers on a form or mandrel and thenisostatically compacting the desired metal powder into it to form thecomposite. Metal spraying or other powder metallurgical techniques canalso be employed to prepare the composite. The ends of the container canbe prepared by conventional powder metallurgical techniques ofcompacting and sintering or hot pressing a mixture of aligned fibers andmetal powders. Should proper alignment of fibers prove difficult itshould be possible to orient the fibers by a working process such asrolling. The volume percent of fibers can be controlled to any desiredamount, between 10-20 percent being most desirable. The thickness of thewall may be from 30 to 50 one-thousandths of an inch thick.

It is to be understood that certain changes, alterations, modificationsand substitutions can be made in this invention without departing fromthe spirit and scope of the depending claims.

What is claimed is:

1. A metal-fiber composite container for helium generatingradioisotopes, comprising helium impermeable metallic wall means forsaid container, and helium permeable quartz fibers integrallyreinforcing the same, said reinforcing quartz fibers extendingcontinuously through at least a portion of said wall means and providinga fibrous helium leak path.

2. The container of claim 1, wherein said metallic wall means arecomprised of a member selected from the group consisting of molybdenum,tungsten, tantalum, columbium, titanium, nickel, cobalt, alloys basedupon the foregoing metals, noble metals, and alloys based upon the noblemetals.

3. The container ofclaim 2, wherein the metallic wall means arecomprised of molybdenum.

4. The container of claim 2, wherein the metallic wall means arecomprised of tungsten.

5. The container of claim 2, wherein the metallic wall means arecomprised of tantalum.

6. The container ofclaim 2, wherein the metallic wall means arecomprised of columbium.

7. The container of claim 2, wherein the metallic wall means arecomprised of titanium.

13. The container of claim 10, wherein the metallic wall means arecomprised of platinum.

14. The container of claim 2, wherein the metallic wall means arecomprised of platinum-rhodium.

15. The container of claim 2, wherein the metallic wall means arecomprised of platinum-iridium.

16. The container of claim 2, wherein the metallic wall means arecomprised of platinum-osmium.

2. The container of claim 1, wherein said metallic wall means are comprised of a member selected from the group consisting of molybdenum, tungsten, tantalum, columbium, titanium, nickel, cobalt, alloys based upon the foregoing metals, noble metals, and alloys based upon the noble metals.
 3. The container of claim 2, wherein the metallic wall means are comprised of molybdenum.
 4. The container of claim 2, wherein the metallic wall means are comprised of tungsten.
 5. The container of claim 2, wherein the metallic wall means are comprised of tantalum.
 6. The container of claim 2, wherein the metallic wall means are comprised of columbium.
 7. The container of claim 2, wherein the metallic wall means are comprised of titanium.
 8. The container of claim 2, wherein the metallic wall means are comprised of nickel.
 9. The container of claim 2, wherein the metallic wall means are comprised of cobalt.
 10. The container of claim 2, wherein the metallic wall means are comprised of a noble metal.
 11. The container of claim 10, wherein the metallic wall means are comprised of gold.
 12. The container of claim 10, wherein the metallic wall means are comprised of silver.
 13. The container of claim 10, wherein the metallic wall means are comprised of platinum.
 14. The container of claim 2, wherein the metallic wall means are comprised of platinum-rhodium.
 15. The container of claim 2, wherein the metallic wall means are comprised of platinum-iridium.
 16. The container of claim 2, wherein the metallic wall means are comprised of platinum-osmium. 